New Caledonia is a large South Pacific island off the east coast of Australia which has been under French administration since 1853. It contains unique flora and fauna which have evolved in isolation for more than 80 million years.

The ability to develop and improve tools is what some claim makes humans unique, said Dr Russell Gray, a member of the New Zealand research team. "Because, to make this level of tool, we need high fidelity sort of learning," he told ABC Science Online. "These tools are way more sophisticated than those used by our closest relative."

Pandanus is a tropical plant with long leaves that are serrated down the edge with barbs that are hooked. The crows, Corvus moneduloides, use their beaks to make a number of tears down the edge of the leaf. They then move down the leaf and tear back the other way. "What you get is a tool that is narrow at the tip and wide at the base with hooks or barbs on the end," said Gray.

The pointed end can get into crevices but the tool is still strong at the wide end which the crows hold with their beak. While other animals do make tools, they are very primitive. Chimpanzees use sticks to dig out termites and Galapagos finches pull spines off cacti to dig out insects. "These are very rudimentary," said Gray. "They have nothing like the same degree of shaping that the crow tool has."

Chimpanzees don't seem to understand the functionality of the physical properties of tools. The crows possibly have a better understanding of the physics of objects and their deployment, he said.

When the crows tear out their tools, they leave behind a cut-out of the tool in the leaf, called a counterpart. This means that instead of having to catch crows in the act, the researchers can estimate the numbers of tools being created simply by counting the 'counterparts'.

Fellow researcher Dr Gavin Hunt spent time in New Caledonia, sampling pandanus trees from 21 sites, and came back with 5,000 samples. On most of the island, the tapered tool was used; but in two areas the tool was different.

"In a smaller region in the south, they made just an untapered narrow strip," said Gray. "In another area they made wide strips that also were not tapered."

This geographic difference in the type of tools made is important because it indicates an evolution in the tool. "This looks like a case of technological evolution increment in the design of tools," Gray said.

The scientists cannot say over what time-frame the tool was developed, but counterparts collected over a 10-year period have not changed greatly.

They will return to New Caledonia this year to investigate how the crows learn to make the tools. "We strongly suspect that it is passed on by social learning," said Gray. "The juveniles follow the adults very closely.

"Only the New Caledonian crows seem to exhibit this level of tool manufacture and use," he added. The crow species which caused a sensation last year at the University of Oxford in Britain by creating a hooked tool out of a piece of wire (see story below) is the same species of bird.